Evaluation location: Colorado, United States
2009 Rhizoctonia Nursery - Experiment
The nursery was planted as a randomized complete-block design with five replications in one-row plots (76 cm row spacing) 4 m long. The field had been planted to sugar beet in 2001 and fallowed in following years with the exception of barley in 2004. The soil (Garrett loam, 0 to 1 % slope, pH 7.8) was fumigated with Telone? II in late Oct 08 for control of soilborne diseases and pests. Manure was applied and roller harrowed in Nov 08. The field was leveled and bedded in May 09. Planting occurred on 22 May, fertilized with 13.6 kg A-1 of ESN? (Agrium Advanced Technologies, Sylacauga, AL), and furrow irrigated as needed. The field was thinned (20-25 cm spacing) and hand weeded 26-28 Jun, and again on 9 Aug. Cultivations occurred on 30 Jun and 21 Jul. Inoculum of R. solani isolate R-9 (AG-2-2), colonized to dry barley and course ground, was applied to the crown of plants on 22-23 Jul at a rate of 4.8 g m-1. A Gandy? applicator was used to apply inoculum and the field cultivated afterwards to place soil onto plant crowns. On 18 Sep beets were lifted and each root rated on a scale of 0 (no damage) to 7 (dead plant with root completely rotted). Average disease severity was determined to create a disease index (DI) for each entry. The scores were adjusted to a 1 (healthy) to 9 (dead) scale: [DI*(9/8)]+1. This was an unusual year for rainfall with 10 cm of rain occurring between 1 Jan and planting providing a full profile at planting. Above average rainfall occurred through Jun and into Jul providing an additional 17.6 cm precipitation. Daytime temperatures remained at sufficient levels for disease development (25-35oC). Rhizoctonia crown and root rot pressure was high and disease development on resistant and susceptible checks was as expected. All experiments in the nursery had significant differences among DI with the most resistant line in the test (which included 7additional trials than the one reported here) having a DI of 1.8 (data not shown), and the most susceptible line a DI of 7.0. This year, a DI of less than 5.0 is considered to indicate some resistance to Rhizoctonia crown and root rot. Next year selections from within those populations will be made and the resistant plants crossed to sugar beet germplasm.
This is reported in: Panella, L., Fenwick, A. L., Hill, A. L., Vagher, T., and Webb, K. M. 2010. Rhizoctonia crown and root rot resistance of Beta PI from the USDA-ARS NPGS, 2009 Plant Disease Management Reports 4:FC004. Online publication. doi:10.1094/PDMR04.